Building flood control rule curves (FCRC) for multipurpose multireservoir systems involves treating simultaneously the stochasticity of future inflows and the multivariate aspect of the problem. The study demonstrates how theoretical findings concerning flood control multireservoir systems regulation obtained by Marien (1984) (the so-called controllability conditions) can be used to build generalized FCRC in multipurpose multireservoir systems. These FCRC are generalized FCRC in the sense that they consist of a time varying constraint set on the needed empty space provisions in the different reservoirs of the system. The applicability of the proposed technique is enhanced by the derivation of new controllability conditions for systems with more than one flood control section and mandatory releases. By means of several examples, it is shown how the proposed methodology is superior to the approach which consists of lumping all the reservoirs of the system into a single imaginary reservoir. A practical example with an eight-reservoir hydropower system in Brazil demonstrates the applicability of the methodology.